is the process of producing cellular energy involving oxygen Cells break down food in the mitochondria in a long multistep process that produces roughly 36 ATP The first step in is glycolysis ID: 778252
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Slide1
RESPIRATION
Slide2Aerobic respiration
is the process of producing cellular energy involving oxygen. Cells break down food in the mitochondria in a long, multistep process that produces roughly 36 ATP. The first step in is
glycolysis
, the second is the citric acid cycle and the third is the electron transport system.
Anaerobic respiration
occurs when the amount of oxygen available is too low to support the process of aerobic
respiration
. There are two main types of
anaerobic respiration
, alcoholic
fermentation
and lactic acid
fermentation
.
Slide3Anaerobic respiration
is
respiration
using electron acceptors other than molecular oxygen (O
2
). In aerobic organisms undergoing
respiration
, electrons are shuttled to an electron transport chain, and the final electron acceptor is oxygen.
It produces lactic acid, rather than carbon dioxide and water.
In aerobic organisms undergoing respiration, electrons are shuttled to an electron transport chain, and the final electron acceptor is oxygen. Molecular oxygen is a highly oxidizing agent and, therefore, is an excellent electron acceptor. In anaerobes other less-oxidizing substances such as
sulphate
(SO
4
2−
), nitrate (NO
3
−
),
sulphur
(S), or
fumarate
are used. These terminal electron acceptors have smaller reduction potentials than O
2
, meaning that less energy is released per oxidized molecule. Therefore, generally speaking, anaerobic respiration is less efficient than aerobic.
Slide4Anaerobic respiration takes place in the cytoplasm of cells. Indeed, most cells that use anaerobic respiration are bacteria or
archaea
, which don’t have specialized organelles
Both
aerobic
and
anaerobic respiration
involve chemical reactions which take place in the cell to produce energy, which is needed for active processes.
Aerobic respiration
takes place in the mitochondria and requires oxygen and glucose, and produces carbon dioxide, water, and energy.
Slide5Cellular respiration (both aerobic and anaerobic)
utilizes highly reduced chemical compounds such as NADH and FADH2 (for example produced during
glycolysis
and the citric acid cycle) to establish an electrochemical gradient (often a proton gradient) across a membrane, resulting in an electrical potential or ion concentration difference across the membrane. The reduced chemical compounds are oxidized by a series of respiratory
integra
membrane proteins with sequentially increasing reduction potentials with the final electron acceptor being oxygen (in aerobic respiration) or another chemical substance (in anaerobic respiration). A proton motive force drives protons down the gradient (across the membrane) through the proton channel of ATP
synthase
. The resulting current drives ATP synthesis from ADP and inorganic phosphate.
Slide6Fermentation,
in contrast, does not utilize an electrochemical gradient. Fermentation instead only uses substrate-level
phosphorylation
to produce ATP. The electron acceptor NAD+ is regenerated from NADH formed in oxidative steps of the fermentation pathway by the reduction of oxidized compounds. These oxidized compounds are often formed during the fermentation pathway itself, but may also be external. For example, in
homofermentative
lactic acid bacteria, NADH formed during the oxidation of glyceraldehyde-3-phosphateis oxidized back to NAD+ by the reduction of
pyruvate
to lactic acid at a later stage in the pathway. In yeast, acetaldehyde is reduced to ethanol to regenerate NAD+. The two processes thus generate ATP in very different ways, and the terms should not be treated as synonyms.
Slide7Along with photosynthesis and aerobic respiration, fermentation is a way of extracting energy from molecules, but it is the only one common to all bacteria and eukaryotes. It is therefore considered the oldest metabolic pathway, suitable for an environment that does not yet have oxygen. Yeast, a form of fungus, occurs in almost any environment capable of supporting microbes, from the skins of fruits to the guts of insects and mammals and the deep ocean, and they harvest sugar-rich materials to produce ethanol and carbon dioxide.
Slide8Types of Anaerobic Respiration
Lactic acid
fermentation
– In this type of anaerobic respiration, glucose is split into two molecules of lactic acid to produce two ATP.
C
6
H
12
O
6
(glucose)+ 2 ADP + 2 phosphate → 2 lactic acid + 2 ATP
Alcoholic fermentation
– In this type of anaerobic respiration, glucose is split into ethanol, or ethyl alcohol. This process also produces two ATP per sugar molecule
C
6
H
12
O
6
(glucose) + 2 ADP + 2 phosphate → 2 C
2
H
5
OH (ethanol) + 2 CO
2
+ 2 ATP
Other types of fermentation
– Other types of fermentation are performed by some bacteria and
archaea
. These include
proprionic
acid fermentation, butyric acid fermentation,
solvent
fermentation, mixed acid fermentation,
butanediol
fermentation,
Stickland
fermentation,
acetogenesis
, and
methanogenesis
.
Slide9Examples of Anaerobic Respiration
Sore Muscles and Lactic Acid
During intense exercise, our muscles use oxygen to produce ATP faster than we can supply
it.When
this happens,
muscle
cells can perform
glycolysis
faster than they can supply oxygen to the mitochondrial electron transport
chain.The
result is that lactic acid fermentation occurs within our cells – and after prolonged exercise, the built-up lactic acid can make our muscles sore!
Yeasts and Alcoholic Drinks
Alcoholic drinks such as wine and whiskey are typically produced by bottling yeasts – which perform alcoholic fermentation – with a
solution
of sugar and other flavoring
compounds.Yeasts
can use complex carbohydrates including those found in potatoes, grapes, corn, and many other grains, as sources of
sugar.Putting
the yeast and its fuel source in an airtight bottle ensures that there will not be enough oxygen around to interfere with the anaerobic respiration that produces the
alcohol!Alcohol
is actually toxic to the yeasts that produce it – when alcohol concentrations become high enough, the yeast will begin to die.
Slide10Swiss Cheese and
Propionic
Acid
Propionic
acid fermentation gives Swiss cheese its distinctive flavor. The holes in Swiss cheese are actually made by bubbles of carbon dioxide gas released as a waste product of a bacteria that uses
propionic
acid fermentation.
Vinegar and
Acetogenesis
Bacteria that perform
acetogenesis
are responsible for the making of vinegar, which consists mainly of acetic acid. Vinegar actually requires two fermentation processes, because the bacteria that make acetic acid require alcohol as fuel!
Glycolysis
is the process by which glucose is broken down
anaerobically
into incompletely oxidized compounds like
pyruvate
, a process which is usually coupled to the synthesis of 2 ATP and 2 NADH for every one glucose molecule processed.
ED pathway
occurs only in prokaryotes and it uses 6-phosphogluconate
dehydratase
and 2-keto-3-deoxyphosphogluconate
aldolase
to create
pyruvate
from glucose. ED pathway
produces only one ATP per glucose—half as much as the EMP
pathway
. ...
Slide15The
pentose phosphate pathway
(PPP; also
called
the
phosphogluconate
pathway
and the
hexose
monophosphate
shunt
) is a process that breaks down glucose-6-
phosphate
into NADPH and
pentoses
(5-carbon sugars) for use in downstream biological processes. ... During this process two molecules of
NADP
+
are
reduced to NADPH. The pathway is especially important in red blood cells (erythrocytes).
Slide16There are two distinct phases in the pathway. The first is the oxidative phase, in which NADPH is generated, and the second is the non-oxidative synthesis of 5-carbon sugars. For most organisms, the pentose phosphate pathway takes place in the
cytosol
; in plants, most steps take place in plastid.
Similar to
glycolysis
, the pentose phosphate pathway appears to have a very ancient evolutionary origin. The reactions of this pathway are mostly enzyme-catalyzed in modern cells, however, they also occur non-
enzymatically
under conditions that replicate those of the
Archean
ocean, and are catalyzed by metal ions, particularly ferrous ions (Fe(II)). This suggests that the origins of the pathway could date back to the
prebiotic
world.